Fiona, the baby hippo, helps celebrate couple's engagement

An unplanned photobomb

Fiona, the famed baby hippo at the Cincinnati Zoo, photobombed a wedding proposal earlier this month. (Hayley Roll/Instagram via CNN video)

Just when you think Fiona, the baby hippo born six months premature at the Cincinnati Zoo, couldn't get any cuter, the international phenomenon took center stage when two of her fans got engaged last week.

Hayley Roll and Nick Kelble were at the zoo to celebrate their one-year anniversary as a couple and stopped by the zoo's Hippo Cove to get their picture taken with Fiona.

After waiting in line for their photo opp, Hayley handed her cell phone to a stranger, who captured the moment when Kelble got down on one knee and popped the question -- with Fiona watching through the glass.

Roll told the Daily Buzz the proposal caught her by surprise, and the photobomb by Fiona wasn't planned either. The couple had been following Fiona's plight since she was born dangerously early in February, setting off a life-and-death struggle that went viral.

Today, Fiona weighs more than 500 pounds, and her legions of fans worldwide can follow her progress via a Facebook TV show broadcast by her keepers at the Cincinnati Zoo & Botanical Garden.

As for the happy couple, Roll and Kelbe plan to wait until 2019  to get married.